Method of making spark plugs



Oct. l0, 1944. E` D ROLLERT 2,360,279-

METHOD 0F MAKING SPARK PLUGS j Filed April 22, 1 .942

`II I |will im -LFI'IH i 594 @95 @fw llll M IIll Bg w m 9L GttornegsPatented Oct. l0, 1944 METHOD OF MAKING SPARK PLUGS Edward D. Rollert,Flint, Michi, assignor to General Motors Corporation, Detroit, Mich., acorporation ot Delaware,

Application April 22, i942, Serial No. 439,992

2 Claims.

This invention relates to a method of securing a grounded electrode tothe shell casing of a spark plus.

Engineers in the spark plug industry have always been faced with aconsiderable problem in the design of the grounded electrode. portantthat this electrode be well secured to the shell casing to provide amaximum of mechanical strength and it is also important that goodcontact between this electrode and the casing be maintained so that theelectrical and heat conductivity from the grounded electrode to theshell casing be maintained at a high value. Spark plug electrodesareexposed to extremely high temperatures in the normal use of the plug.The temperatures have recently been increased due to rising cylinderpressures. The heat resulting from these high temperatures must bedissipated by ilowing to the shell casing, whence it flows to the enginecylinder and is dissipated in the engine cooling system. It is thereforeimportant that the heat conductivity of the joint between the electrodeand the shell casing be maintained at a high level. 'I'his isparticularly true in the production of modern aircraft where highcylinder pressures are utilized to lower the weight per horse powerratio.

It is the object of this invention to provide a spark plug having ashell casing to which the grounded electrode is welded for a maximum ofmechanical strength, and high electrical and high heat conductivity. Itis a further object of the invention to provide a method of weldingwhich does not result in the formation of a flash on the inside of theshell casing, where access to the flash for its -removal would beextremely difficult. This method provides a iiash trap into which themolten metal of the nash may flow, preventingV inward radial flow of theilash which would have to be removed to prevent interference with orimpairment of the eiiicieney of the plug.

Figure l oi' the drawing shows a view in elevation, with parts brokenaway and in section, of a spark plug shell casing and the groundedelectrode before the two have been welded together.

Figure 2 Is a view of the construction of Figure 1 after the weld hasbeen completed.

Figures 3, 4 and 5 show a simplification of the type of weld shown inFigure 2. Figure 3 is a view of the assembly before welding, Figure 4 isa view after the weld has been completed, showing the external iiash,and Figure 5 is a view of the completed shell casing and groundelectrode with the external iiash removed.

It is im-` Figures 6 and 7 show another embodiment of the invention inwhich Figure 6 shows the parts before welding and Figure I shows themafter Welding.

Figures 8 and 9 show still another embodiment of the invention; Figure 8shows the parts before Welding, and Figure 9 shows them after Welding.

Figure.10 is a bottom plan view'of the shell casing shown in Figures 8and 9.

In the embodiment shown in Figures 1 and 2, a shell casing I0 having alongitudinal opening or bore I2 therethrough is shown. 'I'he annularface I4 at the firing end of the shell casing is provided with a recessor counterbore I6. At the bottom of the counterbore an annular groove I8is provided. This groove and bore I2 together denne a ridge 20. Bore I2is preferably relieved or rounded at its firing end as indicated at, 2l.

An electrode 22, which may be of a metal having a high-temperaturecorrosion resistance which is much better than the material of shellcasing I0, is provided to seat in recess or counterbore Iii.` The bottomof the counterbore is pref-- erably beveled as shown at 24 to provideline contact between shell casing I0 and electrode 22 as indicated at26. Furthermore, so that there may be contact between the casing and theelectrode at 26 and not between annular ridge 20 30 and electrode 22,annular ridge 20 is cut down a little so as not to make contact with theelectrode. The Weld will'therefore begin to form at contact line 26.Metal from the electrode 22 will iiow into groove I8, filling it asindicated at 28 of Figure 2. It should be pointed out here that thebevel 24 of the bottom of countersink IS has been exaggerated forpurposes of illustration.

The angle which the bevel 24 makes with the horizontal may vary from 0to 10, preferably from 5 to 7. The clearance between the end of annularridge 20 and electrode 22 will preferably be of the order of magnitudeof .002*to .007 inch.

As is indicated in Figure 2, the iiash trap formed by annular groove I8substantially eliminates the formation of a welding ash on the inside ofbore I2 at the point where electrode 22 is joined to casing I 0. It isalso evident from a study of Figure 2 that the counterbore I6 presentsnumerous advantages. One of these is that there is substantially noexternal flash. 'I'here is therefore no need to eliminate fused metalalong an `outside diameter. More of this will be brought outsubsequently. It is also evident from Figure 2 that this form has theadvantage of providing the same material along the entire length ofcasing l so that no diiiculty is encountered in machining the exteriorof the casing I0 so long as the depth does not exceed the thickness ofthe casing remaining at the end after. the counterbore has been made.This advantage is of particular significance when it is considered thatshell easings are conventionally threaded to engage the spark plugopening in the cylinder block.

Figure 3 is a simplification of Figure 1, in that casing lll is notcounterbored. Electrode 30 extends substantially across the entire endof casing l0. Annular groove I8 is provided as before to furnish a flash`trap to receive metal of electrode 30 as indicated at 32 of Figures 4and 5. The annular face at the firing end of the shell casing may betapered in this case also, in a manner similar to that of Figure 1, asindicated by 34 of Figure 3. Similarly, some clearance is preferablyprovided between the annular ridge 20 and electrode 30. As in Figures 1and 2, opening I2 is relieved or rounded at the firing end, as indicatedin Figure 3 by 2|.

In connection with the embodiment shown in Figures 1 and 2 it was statedabove that counterbore I 6 had the advantage of eliminating any externalflash. The simplified embodiment shown in Figures 3, 4, and 5illustrates the external fiash 36 formed in this embodiment of theinvention and which is eliminated by the use of a counterbore as shownin Figures 1 and 2. Flash 36 vmay be removed by any well known machiningprocess such as cutting, grinding, or the like. Also as stated inconnection with Figures 1 and 2, the embodiment shown in Figures 3-5 hasthe disadvantage of presenting machining diiilculties where the materialof electrode 30 is extremely tough or diicult to machine as where athreading operation is performed after removal of the flash 38. However,flash 36 is nevertheless external and is readily accessible for thenecessary machining process, but an internal iiash would be far lessaccessible. It should be noted that the flash trap of Figures 3-5prevents the formation of an internal flash ina manner similar to thatof flash Itrap shown in Figures 1 and 2.

With some types of alloys, it may be found that there is considerablesputtering or spitting of the metal at the time of the weld. In the twoembodiments of Figures 1 and 3, such spitting or sputtering would takeplace radially inward from contact line 26 right through the clearancebetween annular ridge 20 and elec` trode 22 or 3U. This spitting orsputtering might result in the formation of some internal flash which insome cases might be sumcient to impair the efficiency of the finishedplug. To make such spitting or sputtering impossible or unlikely, Ihave-provided the embodiment shown in Figures 6-9. In the embodiment ofFigure 6, the annular groove I8 issubstantially as shown in the otherembodiments.- However, annular ridge 20 extends toward electrode 22'actually beyond contact line 26'. In order, however, that preliminarycontact be maintained at contact line 26 rather than between annularridge 20 and electrode 22', electrode 22 has been recessed as indicatedat 38 of Figure 6. This recess may take the form of a groove as shown inFigure 6 or merely a relieved iiat as indicated at 40 oi' Figure 8. Itwill be seen, therefore, that annular ridge 20 Wil serve to dam or stopthe flow of any metal spitting radially inward from contact line 26,thus preventing the formation of any inner iiash. The finished weld ofthese ernbodiments is shown in Figures 7 and 9. It will be seen from astudy of these figures that annular groove or flash trap I8 issubstantially iilled in by metal of theelectrodes 22 and 30' asindicated at 28 and 32' respectively. The embodiment of the flash trapshown in Figures 6 and 7 has been indicated as applied in the case of anelectrode welded in a counterbore, whereas the embodiment of Figures 8and 9 has been shown as applied to an electrode welded directly acrossthe firing end ofthe shell casing. It will, of course be understood tothose skilled in the art that the flash trap embodiment of Figures 6 and7 is not restricted to a counterbored shell casing and that theembodiment of the iiash trap shown in Figures 8 and 9 may equally wellbe used where the shell casing is counterbored and the electrode iswelded thereto in the counterbore.

It will, of course, be understood that the welding referred to above andin the following claims refers to forms of welding which result in theformation of iiash.

I claim:

1. In spark plug manufacture, forming a metal shell casing having alongitudinal opening and having at one end an annular face lying gener..ally in a plane, forming a. groove in said annular face', providing aridge inwardly of the groove and projecting beyond the plane of theannular face and welding an electrode to the grooved face of the shellcasing, said electrode having an outer peripheral portion of not greaterdimensions than the external periphery of the annular face and arelieved4 portion receiving said ridge and spaced therefrom, saidwelding operation causing metal from the electrode to flll in the groovein the annular face and to be trapped therein, and said ridge andrelieved por` tion cooperating during the welding operation to preventinward ow of flash.

2. In spark plug manufacture, forming a metal shell casing having alongitudinal opening therethrough and having at one end an annular facelying generally in a plane, relieving the inner edge of the annularface, forming an annular groove in the annular face between the relievedinner edge of the annular face and the outer edge thereof, providing aridge inwardly of the groove and projecting beyond the plane of theannular face and welding an electrode to the grooved face of the shellcasing, said electrode having an outer peripheral portion of not greaterdimensions than the external periphery of the .annular face and arelieved portion receiving said ridge and spaced therefrom, said weldingoperation causing metal from the electrode to fill in the groove in theannular face and -to be trapped therein, and said ridge and the relievedportion in the electrode presenting a tortuous path whereby inward ow ofvflash is restricted.`

EDWARD D. ROLLERT.

